Shifting layup method for structural composite components with complex surface geometry and non-linear fiber path

ABSTRACT

Shifting is a method for manipulating unidirectional non-crimp fabrics that allows for a curved fiber path along with compound surface geometry. The bases for shifting is understanding unidirectional (UD) non-crimp-fabrics (NCFs) as a semi-flexible prismatic linkage and planning manipulations such that the array of linkages can conform to the surface geometry and path plan within allowable manufacturing tolerances. This has applications in structural composite components such as the current trailing edge prefabricated unidirectional components for wind turbine blades, and for future wind turbine blade designs including a curve-linear spar cap.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of and claims the benefit of priorityunder 35 USC 120 to U.S. patent application Ser. No. 16/130,545 filedSep. 13, 2018, which claims the benefit under 35 USC 119 of priority toU.S. Provisional Application No. 62/682,622 filed Jun. 8, 2018, theentire contents of each are hereby incorporated by reference.

BACKGROUND OF THE DISCLOSED SUBJECT MATTER Field of the DisclosedSubject Matter

The disclosed subject matter relates to a system and correspondingmethod for the automation of fiber reinforced polymer compositemanufacturing, e.g., wind turbine blades. Particularly, the presentdisclosed subject matter converts the traditional layup process in windblade manufacturing to a semi-automated assembly line-type process. Thesystem disclosed herein describes a shifting technique to automate themanipulation and layup process of non-crimp fabric (NCF).

Description of Related Art

A variety of methods and systems are known for the manufacture of windturbine blades. Generally, Vacuum Assisted Resin Transfer Molding(VARTM) process is widely used in the manufacture of wind turbine bladesbecause of the lower cost compared to autoclaving.

The process begins with the application of dry fiber that is placed intothe mold, which is referred to as the layup process. However, because ofthe flexibility of the fiber and non-prismatic geometries of the mold,layup is a very labor-intensive manual process; owing to the panel sizesand shear amount of fiber that needs to be placed.

During the layup process, 2D panels of fabric are manipulated manuallyin order to conform to the shape of the 3D mold; simply referred to asdraping. When manipulating the fabric, the workers have to make manyhand motions to the fabric to make sure that the fabric is in contactwith the mold. If the fabric ply fails to be in contact with the mold,out-of-plane deformation will occur and can be considered as a defect ifit is too severe. These hand motions are very difficult to replicatewith a machine because the movements are sensory based and are not thesame for multiple replications. The human interaction involvedintroduces error and variability to the layup process; additionally, theconsiderable labor and training on the layup process drives up the costof the parts.

As evident from the related art, conventional layup methods oftenrequire significant amounts of human interaction and specializedtraining. There thus remains a need for an efficient and economic methodand system for the automatic of the layup process that avoids theaforementioned costs.

SUMMARY OF THE DISCLOSED SUBJECT MATTER

The purpose and advantages of the disclosed subject matter will be setforth in and apparent from the description that follows, as well as willbe learned by practice of the disclosed subject matter. Additionaladvantages of the disclosed subject matter will be realized and attainedby the methods and systems particularly pointed out in the writtendescription and claims hereof, as well as from the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the disclosed subject matter, as embodied and broadly described, thedisclosed subject matter includes a method of fabricating a compositefabric comprising: providing a continuous supply of composite non-crimpmaterial; feeding the continuous supply of composite non-crimp materialthrough at least one pair of rollers, the rollers having an arcuateouter surface configured to engage the continuous supply of compositematerial; performing a shifting operation on the continuous supply ofcomposite material, the shifting operation performed continuously andsynchronized with the feeding step; and depositing the shifted compositenon-crimp material into a mold for a wind blade.

In some embodiments, the shifting operation forms a curve-linear sparcap and is achieved by feeding the laminate through two in-line pairs ofrollers. In some embodiments, the external surfaces of the rollers havea curved or arcuate mating surface, e.g. a cylindrical shape, aparabolic shape, a bulbous shape.

In some embodiments, the outfeed roller is powered and the infeed rolleris torque controlled to maintain tension in the supply fabric. The pairof rollers can be synchronized to rotate at the same speed and directionand duration.

In some embodiments, each roller is connected to a frame on a linearaxis drive, which is perpendicular to the feed direction on the plane ofthe supply material fiber.

In some embodiments, the number of shifts is determined by amount ofdegradation of supply material structure.

In some embodiments, a pair of clamps open and close in tandem with therollers.

In some embodiments, a shifting head is configured to shift fabrics ofup to approximately 280 mm in width.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and are intended toprovide further explanation of the disclosed subject matter claimed.

The accompanying drawings, which are incorporated in and constitute partof this specification, are included to illustrate and provide a furtherunderstanding of the method and system of the disclosed subject matter.Together with the description, the drawings serve to explain theprinciples of the disclosed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of various aspects, features, and embodiments ofthe subject matter described herein is provided with reference to theaccompanying drawings, which are briefly described below. The drawingsare illustrative and are not necessarily drawn to scale, with somecomponents and features being exaggerated for clarity. The drawingsillustrate various aspects and features of the present subject matterand may illustrate one or more embodiment(s) or example(s) of thepresent subject matter in whole or in part.

FIG. 1. depicts the process of shifting a layup segment.

FIG. 2. depicts an example layup utilizing shifting.

FIG. 3. depicts the guide curve and the tolerance zones of the layupresulting from the shifting process.

FIG. 4. depicts the start position of a tow.

FIG. 5. depicts the variables of the fabric.

FIG. 6. depicts a shifting path calculation.

FIGS. 7-8 depict the shifting apparatus

FIG. 9 depicts the working procedure of the shifting apparatus.

FIG. 10 depicts a mesoscale view of a shifted fabric.

FIG. 11 depicts the shape of test coupons.

FIG. 12 depicts the effect of discrete shift quantity on fatigue life ofthe coupon.

FIGS. 13A-B depict exemplary rollers for use in a continuous shiftingoperation.

DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

Reference will now be made in detail to exemplary embodiments of thedisclosed subject matter, an example of which is illustrated in theaccompanying drawings. The method and corresponding steps of thedisclosed subject matter will be described in conjunction with thedetailed description of the system.

In the process of extracting the kinetic energy from the wind andtransferring it to the power generators, blades are one of the mostcritical components of wind turbine systems. The geometry, structuralstrength and weight of the blades directly impact the efficiency of theturbine system, designers are continuously attempting to excel theaerodynamic characteristics of the blades while increasing the lengthand lowering the weight of the structure. To keep up with this dynamicdesign environment, fabrication methods are required to undergocontinuous improvements as well. Employing the new emergingmanufacturing technologies along with implementation of leanmanufacturing techniques, the ultimate objectives of wind turbine blademanufacturers are improving the quality of blades while increasing theproductivity and efficiency.

An assembly line-type operation is a semi-automated process in whichsub-tasks are executed in a sequential manner to create an end product.From manufacturing to product development and even management, thismethodology is being vastly employed to increase throughput. An aspectof the disclosed subject matter is to introduce and detail a novelsystem that improves wind blade manufacturing with unique assembly linemethodology.

Manufacturing composite wind turbine blades using resin infusion methodconsists of three main steps; layup, infusion and mold closure. Theformer—layup—is the most human resource intense step and it has the mostsignificant impact on the quality of the final product.

Unidirectional (UD) non-crimp-fabrics (NCFs) are commonly used as mainstructure components in the manufacture of large composite structures(e.g., wind turbine blades). These composite structures commonly requirecomplex geometry, as this is one of the main advantages of usingcomposite materials. This complex geometry can be made up of compoundcurvatures that requires fiber draping to conform the NCF to the desiredsurface.

Layup of curved fiber path components with compound curvature using UDNCFs is difficult to accomplish without creating distortions that reducethe structure of the component. Inherently, the use of a UD NCF requiresthat there be a desired nominal path for the fiber to follow. When thispath becomes non-linear, the combination of the draping to meet thecomplex curvature, and non-linear fiber path can create fiberdistortions that severely reduce the fatigue life of the component.

Processing by hand manipulates the NCF in a way that does not conform tothe prismatic nature of the NCF at a fiber-level and results innon-productive distortions. UD NCF can be understood as a prismatic 4sided linkage with semi-flexible linkages; however, these linkages mustnot violate certain constraints which are related to materialcomposition and the particular application intended. This understandingleads to a controlled manipulation that reflects the prismatic nature ofthe NCF and results in controlled distortions within the path that isdesired.

Improper draping of UD NCF causes severely reduced fatigue life of theoverall component. Currently out-of-plane distortions are understood,and generally unacceptable, but in-plane distortions that are requiredare not consistently produced in a way that can be accounted for,resulting in the manufacture of components of compromised structuralintegrity. Accordingly, the shifting method disclosed herein allows forpath planning and predictable in-plane distortion that can be accountedfor, which in turn can reduce safety factors required in structuralcomponents.

Without a predictable method or good understanding of the distortion ofUD NCFs, and manual, random layup of the material, high drapability,fabrics with a high shear locking angle must be used to create thesestructural components. This requires a lower areal weight in the fabricdue to smaller fiber tows or loose packing and stitching. With theshifting method disclosed herein, a less drapable, and potentiallyhigher areal weight fabric may be used, resulting in reduced amanufacturing cycle.

As disclosed herein, the automated shifting layup preforms the fabric toapproximate the shape of the mold by shifting and then deposits thefabric into the mold. In this way the layup process can be completedwith very little human interaction.

Shifting

A general description of the shifting method as applied to compositelayup segments is provided in “AUTOMATED COMPOSITE FABRIC LAYUP FOR WINDTURBINE BLADES” by Matthew C. Frank, PhD, Siqi Zhu, and Frank E. Peters,PhD; the entire contents of which are hereby incorporated by reference.As described therein, the act of shifting includes clamping the fabricalong fiber's weft directions and translating the free end parallel tothe clamp in order to change the direction of the fiber, asschematically shown in FIG. 1. An exemplary layup segment which hasundergone the shifting operation is depicted in FIG. 2.

A mathematical representation of the shifting method can be denoted by aguide curve, P(u), which defines the nominal center of the fabric.Additionally, the fabric width and placement tolerance are used tocreate a tolerance zone (TZ), as depicted in FIG. 3. To create thesetolerance zones, the guide curve is offset in both directions by onehalf of the fabric width to form the nominal edge location curves. Eachnominal edge location curve is then offset in both directions by theamount of the placement variation allowed in order to form the tolerancecurves. The area around each nominal edge location curve between thetolerance curves is then the acceptable region for the fabric edge,referred to here as Tolerance Zone 1 (TZ 1) and Tolerance Zone 2 (TZ 2).

The beginning position of any tow, j, as seen in FIG. 4, can becalculated as:

${T_{j}^{0}\begin{bmatrix}x \\y\end{bmatrix}} = {{P(0)} + {\left\lbrack {{2\left( {j - 0.5} \right)} - M} \right\rbrack{\omega_{1}\begin{bmatrix}{\cos\;\left( {\beta + \alpha_{1}} \right)} \\{\sin\;\left( {\beta + \alpha_{1}} \right)}\end{bmatrix}}}}$

Where M is the number of tows in the fabric, α₀ is the nominal shearangle, and ω₀ is the tow spacing at α₀. For unidirectional fabrics, α₀is 90°. Also, α₁ is the pre-shear angle. Pre-shear is the shear angle ofthe fabric at the beginning of the layup. This can be changed tominimize the overall shear angle or change the shear angle in specificlocations throughout the layup. All values for α must remain between−α_(c) and α_(c), which represent the negative and positive shear locklimits.

The location of any tow j at the end of any section, i, can berepresented as:

${T_{j}^{i}\begin{bmatrix}x \\y\end{bmatrix}} = {{T_{j}^{i - 1}\begin{bmatrix}x \\y\end{bmatrix}} + {l_{i}\begin{bmatrix}{\cos\;\left( {\beta + \alpha_{i}} \right)} \\{\sin\;\left( {\beta + \alpha_{i}} \right)}\end{bmatrix}}}$

Where l_(i) is the length of each tow in section i, and α_(i) is theshear angle in section i (as shown in FIG. 5).

To determine these values, T₁ ^(i+1) and T_(M) ^(i+1) are evaluatedwithin TZ 1 and TZ 2 respectively. To do this, TZ 2 is translated along[T₁ ^(i)−T_(M) ^(i)] so that T₁ ^(i) and T_(M) ^(i) are at the samepoint. The possible locations for T₁ ^(i+1) are, then, any point between−α_(c) and α_(c) that is visible from T₁ ^(i) without intersecting oneof the four tolerance curves as shown in FIG. 6. The point in thisregion furthest from T₁ ^(i) is then selected as T₁ ^(i+1). From this,l_(i+1), α_(i+1), ω_(i+1), and all other T_(j) ⁺¹ values can becalculated.

FIGS. 7-8 depict exemplary apparatus for performing the shiftingtechnique disclosed herein, which includes a reference sphere, a fabricroll, rear pinch rollers, a shifting clamp, a spacing clamp. The machinedepicted in FIG. 7 consists of two parts, a three-axis gantry system andfour-axis shifting head. The shifting head and gantry system work incoordinated motion to sequentially shift-deform and deposit the shiftedfabric onto a test mold surface. In this exemplary embodiment, theshifting head is configured to shift fabrics of up to 280 mm in width.

The machine creates a shift in a cycle of coordinated motions. In eachcycle, the machine feeds straight fabric from the fabric roll, shiftsthe fabric to a certain shape, deposits the shifted fabric onto the moldand then prepares for the next cycle. Successive cycles of shifting willresult in a piece of fabric with a curved shape. The work procedure ofthe shifting machine is shown in FIG. 9 and explained below.

The operation of the apparatus depicted in FIGS. 7-8 include thefollowing sequence:

-   -   Initialize: The shifting head moves to start position.    -   Step 1: Spacing clamp moves to corresponding position according        to the length of shift section.    -   Step 2: First, both rollers open and both clamps close to grip        the fabric. Next, the gantry moves the entire shifting head to        position the spacing clamp while shifting clamp synchronously        moves the opposite direction to maintain position relative to        the mold. At the same time the spacing clamp moves toward the        back roller to compensate for the length reduction of the        shifted fabric.    -   Step 3: Both clamps open and both rollers close. Next, the        entire frame moves forward to the next shift position as the        rollers feed fabric accordingly. The shifting clamp moves back        to center synchronously. At this point, the cycle is finished        and the next cycle starts from Step 1.

The shifting method disclosed herein is primarily intended forunidirectional fabrics, where the fabric is sequentially constrained andthen rotated about a deformation angle to approximate curvature.Shifting can be conducted in a 2D plane, making the process easier tocontrol and automate, and in some embodiments can be performed in threedimensions directly within a mold, or after a ply kitting process andthen manually placed within the mold.

The methods and systems presented herein may be used for manufacture oflarge composite structures. The disclosed subject matter is particularlysuited for the manufacture of wind turbine blades. For purpose ofexplanation and illustration, and not limitation, an exemplaryembodiment of the system in accordance with the disclosed subject matteris shown in FIG. 7 and is designated generally by reference character100. Similar reference numerals (differentiated by the leading numeral)may be provided among the various views and Figures presented herein todenote functionally corresponding, but not necessarily identicalstructures.

EXEMPLARY EMBODIMENT

In accordance with an aspect of the disclosure, the shifting methoddisclosed herein identifies UD NCF as a prismatic linkage system anddevelops a path planning for a curved path, both of each local layupsegment as well as the global component, that allows for curved surfaceconformance while maintaining the structure of the component by choosingan acceptable number of discrete shifts. In some embodiments, the numberof acceptable shifts is determined by looking at the degradation ofstructure (e.g. predictable based on the fatigue data shown) incomparison with the design requirements (e.g. weight, thickness,structural integrity, etc.) of the component. This can be optimized bychanging the number of layers and the number of shifts. For purpose ofillustration and not limitation, a fabric segment with 10 layers with 3shifts each may have the same strength as 8 layers with 6 shifts each.The second controlling factor is the tolerance of the path provided.More shifts are required to comply with a tighter path tolerance. Thisallows for a close approximation of the curved path along complexgeometry, and greatly reduces the effort required to make the NCF complywith the required geometry.

The shifting method disclosed herein takes advantage of the fiber-levelstructure of the UD NCF to allow for compliance to the fiber pathwithout out-of-plane fiber distortion. Furthermore, the in-planedistortion that is required for the shifting method can be controlled byincreasing the distortion points and offsetting between adjacent layers,as described above with respect to the number of acceptable shifts. Abenefit of this approach is that it allows for the rapid approximationof the fatigue life of a linear structure of the same merits or designspecifications.

Mathematical models can be used to calculate distortion points tosatisfy both the curvature and structure requirements of a component ina predictable manner which can make these components, particularlylarge-scale components such as wind turbine blades, feasible tomanufacture with predictable fatigue life and structure. Anotheradvantage of the disclosed method is that, because the shifting methodis based on a mathematical model, and is repeatable, it also facilitatesautomated methods that produce high repeatability UD NCF components.

In some embodiments the path plan can be carried out manually, in otherembodiments it can be wholly automated or have select portions carriedout automatically. This automation allows for creation of fabric layupfor components that would be difficult or impossible otherwise.Additionally, the system and method disclosed herein generates a pathplan (e.g. based on length, width, thickness inputs) which makes thecomponent easier to manufacture, provides a better structuralunderstanding of the component, and presents a viable solution forautomated manufacturing.

The shifting technique disclosed herein can be employed in themanufacture of various components of a wind turbine blade. For example,the present disclosure can be utilized to produce a curve-linear sparcap, which would be advantageous in that it would facilitateaeroelastically induced bend-twist coupling of a wind turbine blade forload mitigation. Additionally, or alternatively, the shifting methoddisclosed herein can be used to produce a spar cap that has thenecessary fiber path, while also allowing for the necessary complexcurvature of the surface. Furthermore, the shifting method may alsoallow for a better structural confidence in the component.

Currently prefabricated components are used in the trailing edge of windturbine blades to prevent edge-wise bending moments in the blade. Theshifting method could reduce the manufacturing cost of producing thesecomponents by reducing the technique and skill required to place thesefabrics, and increasing the areal weight of the fabric resulting infewer fabric layers in a single component.

FIG. 10 depicts the result on the shifted fabric revealing that most ofthe unidirectional tows were subjected to pure shear, while the towsadjacent to the clamps are subjected to bending. Tow separation in thebent section occurs when the shift angle is close to shear lockinglimit. The deformation is small enough, i.e. within acceptabletolerances for wind blade manufacturing, where shift angle is to be keptwell below shear locking limit for most commonly used fabrics.

Continuous Shifting

In accordance with another aspect of the disclosure, a continuousshifting apparatus and method can be employed (instead of, or inaddition to, the discrete segmented shifts described above which areperformed as separate steps in a cycle).

In this regard, and as demonstrated in FIGS. 11-12, as the number ofdiscrete shifts used is increased, the fatigue life of the laminateapproaches the fatigue life of a linear laminate. Accordingly, by usinga continuous shift, the fatigue life of the laminate can bestatistically similar to that of linear laminate, or at least maximized.Such a continuous shifting technique is advantageous in that itincreases output, and provides greater consistency across the shiftedlayup segments.

In an exemplary embodiment, this continuous shifting is achieved byfeeding the laminate through two in-line pairs of rollers. The rollerscan be formed with a soft/malleable material (e.g. neoprene or rubber)on an external surface (the cores of such rollers can be more rigid ifdesired). The external surfaces of the rollers can be formed with acurved or arcuate mating surface (e.g. cylindrical, bulbous, parabolic,etc.) to engage the feed supply. For purpose of illustration and notlimitation, some exemplary roller shapes are provided in FIG. 13. Thecurved mating surface ensures that a single tow in the fabric serves asthe master as the linear speed of the roller pulling the fabric wouldvary across the width of the fabric. The outfeed roller can be powered,and the pair of rollers synced, while the infeed can be torquecontrolled to maintain tension in the fabric.

Each of these roller pairs can be connected to the machine body on alinear axis drive which is perpendicular to the feed direction on theplane of the fiber. As the drive rollers pull fabric through themachine, the linear axis drives translate accordingly to distort thefabric. This creates a continuous shift through the length of thefabric, based on the path plan.

In some embodiments, the machine body can be mounted to a CNC controlledgantry, or to a robotic arm, so that as the fabric is dispensed from themachine, it would be laid into position on the mold.

While the disclosed subject matter is described herein in terms ofcertain preferred embodiments, those skilled in the art will recognizethat various modifications and improvements may be made to the disclosedsubject matter without departing from the scope thereof. Moreover,although individual features of one embodiment of the disclosed subjectmatter may be discussed herein or shown in the drawings of the oneembodiment and not in other embodiments, it should be apparent thatindividual features of one embodiment may be combined with one or morefeatures of another embodiment or features from a plurality ofembodiments.

In addition to the specific embodiments claimed below, the disclosedsubject matter is also directed to other embodiments having any otherpossible combination of the dependent features claimed below and thosedisclosed above. As such, the particular features presented in thedependent claims and disclosed above can be combined with each other inother manners within the scope of the disclosed subject matter such thatthe disclosed subject matter should be recognized as also specificallydirected to other embodiments having any other possible combinations.Thus, the foregoing description of specific embodiments of the disclosedsubject matter has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit thedisclosed subject matter to those embodiments disclosed.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the method and system of thedisclosed subject matter without departing from the spirit or scope ofthe disclosed subject matter. Thus, it is intended that the disclosedsubject matter include modifications and variations that are within thescope of the appended claims and their equivalents.

1-14. (canceled)
 15. A method of fabricating a composite fabric for awind turbine blade comprising: providing a continuous supply ofunidirectional non-crimp composite material; feeding the continuoussupply of unidirectional non-crimp composite material through at leastone pair of rollers, the rollers having an arcuate outer surfaceconfigured to engage the continuous supply of unidirectional non-crimpcomposite material; performing a shifting operation on the continuoussupply of unidirectional non-crimp composite material, the shiftingoperation performed continuously and synchronized with the feeding step;and depositing the shifted unidirectional non-crimp composite materialinto a mold for a wind turbine blade; forming a plurality of layers ofdeposited the shifted unidirectional non-crimp composite material into acurved configuration; wherein the rollers are connected to a frame on alinear axis drive, which is perpendicular to the feed direction on theplane of the supply material fiber.
 16. The method of claim 15, whereinthe linear axis drive translates as the composite material is fedthrough the rollers.
 17. The method of claim 15, wherein the rollershave a malleable external surface and a rigid core.
 18. The method ofclaim 15, wherein the rollers have a parabolic shape.
 19. The method ofclaim 15, wherein the rollers have a cylindrical shape.
 20. The methodof claim 15, wherein the continuous shifting is achieved by feeding theunidirectional non-crimp composite material through two in-line pairs ofrollers.
 21. The method of claim 15, wherein an outfeed roller ispowered.
 22. The method of claim 15, wherein an infeed roller is torquecontrolled to maintain tension in the unidirectional non-crimp compositematerial.
 23. The method of claim 15, wherein the pair of rollerssynchronized to rotate at the same speed, direction and duration. 24.The method of claim 15, wherein the number of shifts is determined byamount of degradation of supply material structure.
 25. The method ofclaim 15, wherein a pair of clamps open and close in tandem with therollers.
 26. The method of claim 15, wherein a shifting head isconfigured to shift fabrics of up to approximately 280 mm in width. 27.The method of claim 15, wherein the shifting operation forms acurve-linear spar cap.